1. Field of the Invention
The present invention relates to a level conversion circuit and, more specifically, to a level conversion circuit for converting a voltage amplitude of a signal.
2. Description of the Background Art
In recent years, higher integration, size reduction, speeding-up of operations, and a decreased power consumption of a semiconductor device have been further required. Particularly in an LSI (Large Scale Integrated circuit), a decreased voltage of an internal power supply and speeding-up of an operation are both required. A voltage of the internal power supply of the LSI is currently decreased more than an interface voltage of the LSI. Thus, a level conversion circuit is used to convert a voltage amplitude of an output signal of the LSI when a plurality of LSIs are connected to each other. The level conversion circuit is also used when circuits having different power supply voltages are connected to each other in the LSI.
A conventional level conversion circuit for converting a signal having the “L” level of a ground potential GND (0 V) and the “H” level of a power supply potential VDDL (for example, 1.2 V) into a signal having the “L” level of ground potential GND (0 V) and the “H” level of a power supply potential VDDH (for example, 3.3 V) requires a long time to perform a level conversion operation and consumes a large power. In addition, it is difficult to equalize a time required to perform the level conversion operation when an input signal rises from the “L” level to the “H” level with a time required when the input signal falls from the “H” level to the “L” level. When there is a large difference between power supply potential VDDL and power supply potential VDDH, times required for the level conversion operations tend to differ from each other.
Japanese Patent Laying-Open No. 06-209256 discloses a level conversion circuit which can convert 5 V into 1-7 V, and 1-7 V into 5 V. This level conversion circuit has an improved β value (a current amplification factor) of a transistor forming the level conversion circuit.
In addition, Japanese Patent Laying-Open No. 07-086913 discloses a pulse level conversion circuit with reduced current consumption. This pulse level conversion circuit can prevent degradation of a high amplitude output pulse by setting a delay time required for a potential of an output node rising to a high potential.
In addition, Japanese Patent Laying-Open No. 05-308274 discloses a CMOS level shift circuit capable of obtaining a signal output of a high voltage level and a constant current with a circuit construction including an MOS transistor having a small withstand voltage between the gate and a source.
Speeding-up of a level conversion operation and a decreased power consumption, however, are not sufficiently attained with each of Japanese Patent Laying-Open Nos. 06-209256 and 05-308274. In addition, the level conversion circuit of Japanese Patent Laying-Open No. 07-086913 has low versatility because it cannot handle an input signal having a level varying at a low speed.